Core for casting concrete slabs

ABSTRACT

A core for providing noncylindrical passages in long concrete slabs comprise a multi-channel molding of laterally expansible material. A core of suitable length is provided with one or more cylindrical passages for receiving compressed air for lateral expansion purposes. The core section itself may be generally oval with flattened top and bottom faces. In addition to the cylindrical passages for inflation by air, one or more supplemental open air passages for the entire core length are provided. The shape, sectional area and orientation of such supplemental open air passages function to direct over-all lateral expansion of the molding, to maintain substantial congruence between the expanded and normal core shapes.

United States Patent Smith 5] Mar. 14, 1972 [54] CORE FOR CASTINGCONCRETE SLABS [72] Inventor: Robert E. Smith, Dayton, Ohio [73]Assignee: The Flexicore Co., Inc., Dayton, Ohio [22] Filed: Aug. 17,1970 [21 Appl. No.: 64,540

FOREIGN PATENTS OR APPLICATIONS 1,332,072 6/1963 France ..25/l28D458,625 12/1936 Great Britain ..249/65 Primary Examiner-J. SpencerOverholser Assistant Examiner-Ben D. Tobor Attorney-Robert L. Kahn [57]ABSTRACT A core for providing noncylindrieal passages in long concreteslabs comprise a multi-channel molding of laterally expansible material.A core of suitable length is provided with one or more cylindricalpassages for receiving compressed air for lateral expansion purposes.The core section itself may be generally oval with flattened top andbottom faces. In addition to the cylindrical passages for inflation byair, one or more supplemental open air passages for the entire corelength are provided. The shape, sectional area and orientation of suchsupplemental open air passages function to direct over-all lateralexpansion of the molding, to maintain substantial congruence between theexpanded and normal core shapes.

6 Claims, 3 Drawing Figures PATENTEDMAR 14 I972 ROBERT E. SMITH CORE FORCASTING CONCRETE SLABS This invention relates to a non-cylindrical coreconstruction providing correspondingly shaped non-cylindrical passagesthroughout the length of a concrete slab during casting 5 thereof. Slabsto which this invention relate are frequently cast in lengths up to theorder of about 60 feet. Such slabs may be provided in various widths andthicknesses, the width in all such cores being substantially greaterthan the thickness.

Thus slabs of 8 X 16 or 8 X 24 inches in various lengths have been knownfor a long time. As a rule in such slabs, cylindrical passagesthroughout the entire length of a slab are provided not only to save onconcrete but also to improve on the beam characteristics of the castslab. An example'of such a slab is disclosed in U.S. Pat. No. 2,299,111.Such slabs are usually reinforced with long steel strands.

The trend of the art has been in the direction of slabs whose width tothickness ratio is such as to necessitate the use of flattenednon-cylindrical passages. For example, a slab having a thickness of 4 or6 inches with a width up to about 24 inches should have a desired volumeof void to concrete. Providing a multiplicity of cylindrical, laterallyoffset passages in such a slab creates production complications.

In the casting of concrete slabs, a core for creating a passage orchannel must be maintained accurately in position during the casting andcuring process. Since the thickness of concrete between the externalsurfaces of the finished slab and the intemal surface of such slab mustbe accurately controlled to maintain the strength characteristic of thefinished slab, it is not only necessary to control the lateraldimensions of a core throughout the length thereof during casting but inaddition it is necessary to control the location of a core within thecasting form.

It is also desirable to be able to vary somewhat the lateral dimensionsof a core. When a casting form has one or more cores present therein andhas its casting region filled with concrete mix, the form and contents,after vibrating procedure, are cured in a humid atmosphere in a kiln ata temperature of about 160 F. for a suitable time, usually about sevenor eight hours. Prior to filling a form with mix, a core is preferablyhandled in such a fashion as to increase somewhat its lateral dimensionssufficiently so that the enlarged core on both sides of the bulk-headopening creates a seal to retain concrete mix. This lateral enlargement,when accomplished, is usually obtained by inflating with compressed air,assuming the core is susceptible to such treatment. Upon completion ofthe cure the casting form is removed from the kiln and will requirestripping. Before a cured casting is removed from a casting form, it iscustomary to pull out the core or cores, this being accomplished bylongitudinal movement of the cores. Once a core or cores are removed,the cured casting is removed from its form by spreading the sides of theform sufficiently to effect casting release.

Removal of a core from a cured casting involves initially the reductionof the lateral core dimensions to normal or even below normal. When acore has been inflated to effect a desired increase in transversedimensions, the first step is to deflate the core and permit theelasticity of the core to restore the core dimensions to normal. Whenthis occurs, there may be some movement of the core exterior surfacesfrom the interior slab passage walls. However, for the most part,reliance is had, in connection with core removal from the casting, uponthe fact that when a core body is pulled at one end, there will be asignificant elongation of the core body in response to the pull with aconsequent reduction in core transverse dimensions. Sometimes when acore body sticks within a cured slab, it may be advisable to alternatelyinflate and deflate the core to aid in core removal.

In accordance with the present invention, a molded or extruded core ofelastic material is provided with longitudinal passages of two differentshapes. Certain passages have a cylindrical cross section along theentire length of core and are adapted to be sealed so that air at adesired pressure may be introduced, maintained therein or removedtherefrom. 75

When air at a suitable pressure is introduced in such cylindricalpassages, the elastic core body material reacts by lateral expansion. Inaddition to the cylindrical passages for compressed air, the inventionprovides for supplementary air passages throughout the length of thecore. Such supplementary passages are preferably open to atmosphere atall times and function to control the intensity and direction of lateralexpansion forces emanating from the compressed air passages. While suchsupplemental passages in their simplest form are open to atmosphere,they may be considered as providing a generally constant low levelresistance to lateral by directed forces through the core body, theresistance level however being substantially lower than the resistanceof the core material which would normally be present in the absence ofsuch supplementary passages. Instead of leaving such supplementarypassages open to atmosphere, it is possible to seal such passages andhave air therein at some desired low pressure.

The supplementary control passages have such a transverse area and shapeand will have such an orientation as to provide desired lateralexpansion characteristics of the entire core when the cylindricalpassages are filled with compressed air.

The core material itself is preferably of rubber (natural or synthetic)or of plastic material having suitable characteristics with regard toelasticity, flexibility, air retention, chemical inertness, resistanceto ageing and general durability for wear and tear. For the most part,in connection with casting concrete slabs, rubber having a Durometerhardness of the general order of about 70, plus or minus about ID, hasbeen found to be good. The hardness and elasticity may vary dependingupon lateral core dimensions, desired wall thickness, air pressures tobe used and manufacturing tolerances.

The transverse shape of passages for containing compressed air willpreferably be circular although some departure may be perrnissable. Thetransverse shape of the supplementary passages will generally benon-circular and the dimensions, shapes, locationand orientations areselected that a desired wall thickness between the inside wall of acompressed air passage on the one hand and the core exterior or theinside wall of a suitable passage may be kept within limits.

By having a suitable ratio of void to transverse sectional area of theentire core, the weight, lateral expansion characteristics andlongitudinal stretch core characteristics may be adjusted so that as awhole, a long core will have desired characteristics for. use inconnection with creating longitudinal passages in concrete slabs. Byrelying upon a homogenous core material such as rubber for example, acore having an unlimited life may-be provided, the life of such a corebeing generally determined by wear and tear in actual use. Such a coremay be easily handled and will have sufficient longitudinal stretch andelasticity so that removal of a core from a casting may be readilyaccomplished.

In accordance with the present invention, an elongated core ispreferably provided with a header at one end to interconnect thecompressed air inflatable passages within the core and also preferablyincludes means for accurately maintaining the air pressure within thecylindrical core passages to a desired maximum value during the castingand curing operation. Thus, a core having means for equalizing pressureswithin the inflatable core passages will enable an operator to handlethe entire construction as one core, both physically and functionallyinsofar as lateral dimensional expansion and contraction are concerned.

The invention will now be described in connection with the drawingswherein:

FIG. 1 is an exploded perspective view of a core body embodying thepresent invention, certain parts being cut away to illustrate theconstruction must clearly.

FIG. 2 is a transverse section of the core body embodying the presentinvention, the dotted lines illustrating approximately the inflatedshape of the core body.

H6. 3 is a plan view showing the new core body embodying the presentinvention installed in a casting frame, certain parts being cut away-The core body sections illustrated in FIGS. 1 and 2 are shown in adeflated or normal condition and has generally flat top face 10,generally flat bottom face 11 with outwardly curved sides 12 and 13connecting the top and bottom faces of the core. A core body may haveany length up to the order of about 60 feet. The width and thickness ofthe core may be selected as desired. A core body such as illustrated inFIG. 1 may have as many alternate cylindrical passages andnoncylindrical passages, all in laterally offset relation, as desired. Anumber of separate core bodies may be used in laterally spaced relationin a casting form adapted for casting slabs up to any desired width andhaving any desired thickness. For example, U.S. Pat. No. 3,416,272granted Dec. 17, 1968 shows a slab having two separate non-cylindricalpassages in laterally offset relation to which the invention may beapplied during casting of such slabs. As illustrated here, passageshaving circular sections 15, 16 and 17 are provided, the center line ofsuch circular sections lying along a transverse line 19 extending midwaybetween top and bottom faces 10 and l 1.

It is understood that a length of core will have cylindrical passageswith center line 19 being part of a plane. For convenience, however, thevarious portions of the core will be described as shown in section withthe understanding that all such portions of the core will form parts ofplanes and extended surfaces. Halfway between curved sides 12 and 13 isa line 20 extending perpendicularly between 10 and 11 and constituting avertical center line with line 19 functioning as a horizontal centerline.

Depending upon the elasticity of the core body material and therelationship between various dimensions, cylindrical passages 15, 16 and17 are so dimensioned relative to the exterior core surfaces as toprovide for a prescribed wall thickness for as large a portion of thecircumference of each cylinder as possible. As an example with rubberhaving a Durometer of between about 65 and 75, and the dimensionshereinafter given, the wall thickness may be, when deflated, aboutone-fourth of an inch or 16ths. Some portions of wall thickness betweenthe cylindrical passages and top and bottom faces and 1 1 may be greaterthan the wall thickness at sides 12 or 13. The lateral spacing betweenadjacent cylindrical passages and 16 and 17 is great enough so thatnoncylindrical supplementary longitudinal passages 23 and 24 areaccommodated. Each of these supplementary passages 23 and 24 is sodimensioned and so shaped that the intervening wall between cylindricaland non-cylindrical passages are maintained for the most part at thedesired wall thickness. Insofar as all the passages are concerned, bothcylindrical and noncylindrical passages are so dimensioned with respectto outer faces 10 and 11 of the core so that the wall thickness ismaintained along planes parallel to the plane containing center line 20.

Certain regions obvious on inspection will have a substantially greaterwall thickness than what might be termed as normal. In use, if passages15, 16 and 17 are inflated with suitable air pressure, such as forexample 25 or 50 pounds per square inch, while normal atmosphericpressure is maintained in noncylindrical passages 23 and 24, the corematerial will be expanded. The expanded shape of the core under desiredpressure for slab casting is shown in dotted lines. The precise outlineof the core when deflated will not be maintained precisely wheninflated. So long as the core outline and the longitudinal passage in acast slab is maintained constant, precise geometrical congruence neednot necessarily be maintained.

It is possible to modify the shape of non-cylindrical passages 23 and 23so that the four rounded corners of these passages can be extendedoutwardly into the massive wall portions of the core. Sharp corners inthe shapes of sections should be avoided. Some lack of correspondencebetween the deflated and inflated shapes improves the separation of corefrom concrete when deflating of core material occurs.

It is desirable for facilitating the use of a core in a slab castingoperation to provide a common means for introducing air into or removingcompressed air from each of the circular passages. At what might betermed the live end of an entire core, header structure 29 is providedfor fitting into one end of each cylindrical passage 15, 16 and 17. Aheader may be made of plastic, aluminum or other metal and may havevalve 30 and cylindrical stub portions 31, 32 and 33 extending from theheader proper for insertion into the ends of core cylindrical passages.The header and core are firmly secured together by cementing the core tothe header stubs. As an example, epoxy cement may be used to provide atight strong joint. Non-cylindrical core passages 23 and 24 may or maynot be sealed and in any event are maintained at substantially normalatmospheric pressure.

The dead end of each of the cylindrical passages in the core body issealed with suitable plugs 34 extending into the end portions of acircular passage. Such plugs may be of rubber or plastic and should bestrong enough to withstand the compressed air when the core is to beinflated.

In an exemplary structure, the width along line 19 of a core way 7 3/l6ths inches with the thickness between faces 10 and 11 one and 3/16thsinches. The radius of a circular passage was ll/16ths inches while thedistance between centers of passages 15 and 16 was 2 and l l/l6thsinches. The width of non-cylindrical passage 23 along the planecorresponding to center line 19 was ll/l6ths inches. Each corner ofnon-cylindrical passage 23 is generated by a one-fourth inch radiuscurve with the widest portion of such passage about midway betweencenter line 19 and the top or bottom of passage 23 having a width ofabout 13/ l6ths inch. The dimensions given are merely by way of exampleand may be varied.

In order to maintain a substantially constant air pressure within thecylindrical core passages during curing, it is preferred to embody meansfor allowing a fixed rate of escape of compressed air. As is disclosedin US. Pat. No. 3,306,568, excess pressure air relief means are providedwhereby a controlled leakage of air prevents significant increase in airpressure due to the rise in temperature of the core and its air contentduring curing. Any other means for maintaining a generally constant airpressure within the cylindrical air passages in the core may be used.

A core structure when used in a casting form will extend throughbulk-heads defining the ends of the casting region. The rear end portionof a core containing the plugs will not be laterally expanded and shouldtherefore extend beyond a bulk-head. In practice, a solid rubber plugwithin a cylindrical core passage is vulcanized to the rubber corematerial at a passage end and may have a length longitudinally of thecore for about two or three inches, although the exact length isunimportant.

At the front or forward end of a core, the manifold stub portions extendinto the appropriate ends of the cylindrical passages of the core andmay have a length of about Z'kor 3 inches. The entire front end portionof the core body carrying the manifold may extend beyond the livebulk-head outside of a casting form for a distance of 4 or 5 inches. Thecore body when laterally expanded will have laterally expanded portionson both sides of all bulk-heads. The casting form will thus be sealedagainst leakage of concrete. It is possible to have a long core extendthrough several bulk-heads in one long casting form. In all instances,the exterior surface of a core should be smooth and so dimensioned thata core in deflated condition may be moved into or pulled out from thecasting region through bulk-heads. Such a core structure may be easilyand simply handled in a manner generally resembling a conventionalcylindrical core.

A core body of particular dimensions in normal deflated condition may bevariously inflated to somewhat different dimensions, depending upon theair pressure used. Thus it may be possible to increase the over alllateral dimensions of a core by as much as 10 percent to accommodatesome variations in lateral dimensions of the slab passages to beprovided.

A core embodying the present invention is easy to use and can withstandthe rough handling usually present in a plant making concrete slabs. Thenew core has sufficient body so that a long length can be readilyhandled. Most of the expansive force due to compressed air in the corecylindrical passages will be directed to expand the core laterally.While some core elongation may occur in response to air pressure, thiswill be inconsequential due to the great ratio of core length to coretransverse dimensions.

The valve for controlling air flow into or from the header of the coreshould be susceptible to being closed for air retention or being openfor deflation and during core removal from a casting form. The valveshould have sufficient air capacity so that rapid air flow is possible.

While the ratio of void to core sectional area may range over limitsfrom about 25 percent to as much as 70 percent, a preferred range isfrom about 40 percent to about 60 percent. The ratio will determine themagnitude of lateral expansion of a core in response to a definite airpressure. In general, the lateral expansion of a core due to compressedair should be at least in the order of about one-eighth of an inch, thisbeing measured on each side of the vertical and horizontal center planesso that as between the top and bottom faces for example, the totalincrease in core thickness will be about onefourth inch, the same beingtrue for the total width between the curved sides of the core. Upondeflation, a core will tend to return to its normal transversedimensions and thus to an appreciable extent may pull away from theconcrete inner surface of a passageway in the slab. As a rule, such corebehavior will make it easier to pull the core from the casting. When acore is subject to tension, as when pulling, the longitudinal force issufficiently great to cause a decrease in lateral core dimensions.

lclaim:

l. A core for use in casting concrete slabs ranging in length up to asmuch as 60 feet, said core having an elongated body of homogeneouselastic material substantially immune to temperatures of the order ofabout l60 F., said core body having a length sufficiently great so thatportions of said core body may extend through bulk-heads beyond thecasting region, said core body in transverse section being shaped toprovide generally flat top and bottom faces and outwardly curved sidesand a plurality of separate, similar, cylindrical passages in laterallyoffset relation longitudinally of the core lengths, said passages beingbetween top and bottom core faces, said core having a supplementarypassage between each pair of adjacent cylindrical passages, each suchsupplementary passage extending the full length of the core body andhaving a non-circular section, sealing means at one end of each saidcylindrical passage for closing the same, header means at the other endof each said cylindrical passage for interconnecting said passages, saidsupplementary passages being open to atmosphere, said core, when the airpressure within said cylindrical passages is great enough, laterallyexpanding, the relative sectional areas of the various passages and therelative locations of such passages causing said expanded core shape tobe generally congruent to the normal core shape, said core, upon releaseof air in said cylindrical passages, contracting and pulling away fromthe cured concrete so that when said core is pulled from the casting,the normal core contraction, coupled with additional core contractionresulting from tension on said core, incident to removal, facilitatessuch removal.

2. The construction according to claim 1 wherein said core material isof rubber having a Durometer hardness of about 70.

3. The construction according to claim 2 wherein the core wall thicknessabout a major portion of the passages is about 5/ 16th inch whereby airpressure as low as about 25 pounds per square inch may be used.

4. A core construction according to claim 1 wherein said core has amanifold structure with pipe stub portions fitting into the free otherends of cylindrical passages only, each noncylindrical passage beingopen to atmosphere, said core being adapted to be handled as a unitarystructure.

5. A core construction according to claim 1 wherein the ratio of void tocore sectional area may range from about 25 percent to as much as about70 percent.

6. A core construction according to claim 5 wherein the

1. A core for use in casting concrete slabs ranging in length up to asmuch as 60 feet, said core having an elongated body of homogeneouselastic material substantially immune to temperatures of the order ofabout 160* F., said core body having a length sufficiently great so thatportions of said core body may extend through bulk-heads beyond thecasting region, said core body in transverse section being shaped toprovide generally flat top and bottom faces and outwardly curved sidesand a plurality of separate, similar, cylindrical passages in laterallyoffset relation longitudinally of the core lengths, said passages beingbetween top and bottom core faces, said core having a supplementarypassage between each pair of adjacent cylindrical passages, each suchsupplementary passage extending the full length of the core body andhaving a non-circular section, sealing means at one end of each saidcylindrical passage for closing the same, header means at the other endof each said cylindrical passage for interconnecting said passages, saidsupplementary passages being open to atmosphere, said core, when the airpressure within said cylindrical passages is great enough, laterallyexpanding, the relative sectional areas of the various passages and therelative locations of such passages causing said expanded core shape tobe generally congruent to the normal core shape, said core, upon releaseof air in said cylindrical passages, contracting and pulling away fromthe cured concrete so that when said core is pulled from the casting,the normal core contraction, coupled with additional core contractionresulting from tension on said core, incident to removal, facilitatessuch removal.
 2. The construction according to claim 1 wherein said corematerial is of rubber having a Durometer hardness of about
 70. 3. Theconstruction according to claim 2 wherein the core wall thickness abouta major portion of the passages is about 5/16th inch whereby airpressure as low as about 25 pounds per square inch may be used.
 4. Acore construction according to claim 1 wherein said core has a manifoldstructure with pipe stub portions fitting into the free other ends ofcylindrical passages only, each non-cylindrical passage being open toatmosphere, said core being adapted to be handled as a unitarystructure.
 5. A core construction according to claim 1 wherein the ratioof void to core sectional area may range from about 25 percent to asmuch as about 70 percent.
 6. A core construction according to claim 5wherein the ratio of void to core sectional area is from about 40 toabout 60 percent.